This invention relates to a probe for measuring electromagnetic radiation from subcutaneously illuminated living tissue to thereby, for example, provide a measure of oxygen saturation of the tissue. Such a measure in a fetus can provide information as to the health and well-being of the fetus.
The problems encountered in childbirth can in many instances be avoided if the health condition of the fetus can be monitored on a continuous basis. If a change in the health condition is detected, the attending physicians can immediately take actions to correct the situation if possible. One such health condition of interest is the fetal oxygen supply which, of course, should be maintained at proper levels if the most problem free delivery is to be achieved.
A number of approaches have been devised for measuring oxygen supply in the fetus or, more particularly, measuring oxygen saturation in the tissue of the fetus. These approaches typically involve placing a probe of some type in contact with fetal skin and, in some cases, inserting some part of the probe into the skin. Some of these probes are fairly large and therefore cannot be inserted through the cervix into contact with the fetus until significant dilation has taken place. Of course, this would limit the effectiveness and utility of the probe since monitoring could only begin at some time after the delivery process had already begun.
Another approach to measuring oxygen saturation in fetal tissue involves so-called reflectance oximetry. In this approach, the probe is provided with a light source which directs light toward the tissue, and a light detector which detects light reflected from the tissue. The amount of light detected provides a measure of oxygen saturation of the tissue against which the probe is placed. A problem with this approach is that the signal level of detected reflected light is oftentimes poorly modulated, making accurate measurements difficult. This low modulation level in part is caused by scattering of light in the cutaneous layer so that much of the light reflected back to the detector is unmodulated light.